1. Field of the Invention
The present invention relates to a fuel injection device for an internal combustion engine, which uses fuels, each having a different property, in particular, fuels, each containing alcohol at a different rate.
2. Description of the Related Art
The following fuel injection device for an internal combustion engine has been conventionally proposed. When a change in fuel property is detected, a fuel injection quantity is temporarily changed by canceling a limit condition for correction of the fuel injection quantity or expanding an allowable range of the correction. In addition, the fuel property is estimated based on a behavior of an air-fuel ratio, which is detected in an exhaust passage (for example, see JP 2003-120363 A).
According to the conventional fuel injection device for the internal combustion engine disclosed in JP 2003-120363 A, even if the fuel property has greatly changed, an optimal quantity of the fuel may be injected to be supplied, thereby preventing exhaust-gas emission performance from being deteriorated. Moreover, based on the behavior of the air-fuel ratio of an exhaust gas, which is caused by changing the fuel injection quantity, the fuel property may be estimated with high accuracy without providing an additional special sensor.
Moreover, another conventional fuel injection device for the internal combustion engine as follows has also been proposed. In this fuel injection device for the internal combustion engine, even when the estimation of a concentration of a single component in the fuel is inhibited based on an operating state, the estimation of the concentration of the single component in the fuel is allowed if the fuel correction quantity obtained based on the air-fuel ratio is out of a predetermined range (for example, see JP 2004-285972 A).
According to the another conventional fuel injection device for the internal combustion engine disclosed in JP 2004-285972 A, when the fuel correction quantity obtained based on the air-fuel ratio is out of the predetermined range, the estimation of the concentration of the single component in the fuel is allowed. Therefore, by using an estimated concentration value obtained by the estimation, operation performance or exhaust emission performance may be prevented from being deteriorated due to an insufficient correction quantity.
However, the prior art has the following problems. In the above-mentioned conventional fuel injection devices for the internal combustion engine, when a change occurs in the fuel property without being detected, the cancellation of the limit condition for the correction of the fuel injection quantity and the estimation of the fuel property are not performed. Therefore, appropriate control is not performed.
Moreover, as described in JP 2003-120363 A, the limit for the correction of the fuel injection quantity is for limiting the fuel injection quantity so as to prevent the occurrence of an abnormal change in the fuel injection quantity, in view of degradation of components of a fuel injection system such as an injector with elapse of time. When such a great change that the correction of the fuel injection quantity reaches the limit occurs, it is generally judged that the change is due to an abnormality occurring in the fuel injection system. Therefore, if the change in the correction of the fuel injection quantity due to the change in the fuel property is not appropriately controlled, it may be erroneously judged that the abnormality occurs in the fuel injection system.
For example, in the case where the change in the fuel property is detected based on refueling which is determined based on a change in a residual fuel quantity in a fuel tank, the refueling may not be detected because the change in the residual fuel quantity may not be sometimes detected depending on the degree of accuracy of a level sensor for the fuel tank when a small quantity is refueled. As a result, it is considered that the change in the fuel property is not detected either. At this time, if the residual fuel quantity in the fuel tank is large, it is considered that the fuel property is not affected much by the small quantity of refueling. If the residual fuel quantity in the fuel tank is small, however, the fuel property sometimes greatly changes. Therefore, if the control at the time of occurrence of the change in the fuel property is not appropriately performed, the deterioration of exhaust emission performance and insufficient combustion are caused. In addition, there is a fear that it may be erroneously judged that the abnormality has occurred in the fuel injection system. Moreover, for the fuel injection device which learns the amount of correction corresponding to a tolerance and deterioration of each of the components of the fuel system, there is a fear of performing erroneous learning because the correction of the fuel injection quantity based on the change in the fuel property is erroneously reflected to a leaning value.
In the case where the refueling is detected based on opening/closing of a fuel filler lid, it is difficult to immediately detect a failure because a sensor for detecting the opening/closing of the fuel filler lid is generally expected to have a simple structure. Once the failure is detected, it is considered that measures using alternative control or the like may be taken. Until the detection of the failure, however, the detection of the change in the fuel property is not performed in the same manner as described above. The same is applied to the detection of a failure of the level sensor of the fuel tank.
On the other hand, in the another conventional fuel injection device for the internal combustion engine disclosed in JP 2004-285972 A, the estimation of the concentration of the single component in the fuel is allowed when the fuel correction quantity obtained based on the air-fuel ratio is out of the predetermined range. Therefore, even when the air-fuel ratio is changed due to a factor other than the change in the fuel property, the concentration is estimated according to the fuel correction quantity determined based on the change in the air-fuel ratio. As a result, the concentration is erroneously estimated.
Moreover, in the fuel injection device disclosed in JP 2003-120363 A, which judges the occurrence of the abnormality in the fuel injection system when the correction of the injection quantity reaches the limit, the estimation of the concentration and the correction of the fuel injection quantity are performed even if the change in the air-fuel ratio occurs due to the abnormality of the fuel injection system, as described in JP 2004-285972 A. Therefore, even in such a case, it is not judged that the abnormality has occurred in the fuel injection system.